1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for detecting an operation of a downhole tool. More particularly, embodiments of the present invention generally relate to using optical sensing systems to detect an operation of the downhole tool. More particularly still, embodiments of the present invention generally relate to detecting a position of a flow control device.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling the wellbore to a predetermined depth, the drill string and bit are removed. Thereafter, the wellbore is typically lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. It is common to employ more than one string of casing in a wellbore. The casing can be perforated in order to allow the inflow of hydrocarbons into the wellbore. In some instances, a lower portion of the wellbore is left open by not lining the wellbore with casing. To control particle flow from unconsolidated formations, slotted tubulars or well screens are often employed downhole along the uncased portion of the wellbore. A production tubing run into the wellbore typically provides a flow path for hydrocarbons to travel through to a surface of the wellbore.
Controlling a flow of fluid into or out of tubulars at various locations in the wellbore often becomes necessary. For example, the flow from a particular location along the production tubing may need to be restricted due to production of water that can be detrimental to wellbore operations since it decreases the production of oil and must be separated and disposed of at the surface of the well which increases production costs. Flow control devices that restrict inflow or outflow from a tubular can be remotely operated from the surface of the well or another location. For example, the flow control device can comprise a sliding sleeve remotely operable by hydraulic pressure in order to align or misalign a flow port of the sliding sleeve with apertures in a body of the flow control device. This operation can be performed remotely without any intervention, and there is typically no feedback on the actual position or status of the flow control devices within the wellbore.
In wells equipped with electrical sensing systems that rely on the use of electrically operated devices with signals communicated through electrical cables, electrical sensors are available that can determine a position or status of flow control devices. Examples of such devices used to determine positions of flow control devices include linear variable differential transducers (LVDT). However, problems associated with electrical cables include degradation of the cable and significant cable resistance due to long electrical path lengths downhole that require both large power requirements and the use of large cables within a limited space available in production strings. Additionally, electrical sensors comprising inherently complex electronics prone to many different modes of failure must be extremely reliable since early failure may require a very time consuming and expensive well intervention for replacement. There are numerous other problems associated with the transmission of electrical signals within wellbores including difficulties encountered in providing an insulated electrical conductor due to the harsh environment and interferences from electrical noises in some production operations.
Therefore, many wells utilize optical sensing systems equipped with optical fibers and optical sensing techniques capable of measuring thermal changes, pressure changes, and acoustic signals. Unlike electrical sensors, optical sensors lack the ability to directly determine whether a mechanical operation downhole has been performed. For example, optical sensors can not directly determine a position of a sleeve on a flow control device.
Therefore, there exists a need for apparatus and methods that provide real time knowledge of the operation, position, and/or status of downhole tools in wellbores. There exists a further need for apparatus and methods for detecting a mechanical operation of downhole tools utilizing optical sensing systems.